1. Field of the Invention
The present invention relates to resistance mutants of Hepatitis C virus NS3/4A protease.
2. Background of the Related Art
Infection by hepatitis C virus (“HCV”) is a compelling human medical problem. HCV is recognized as the causative agent for most cases of non-A, non-B hepatitis, with an estimated human sero-prevalence of 3% globally [A. Alberti et al., “Natural History of Hepatitis C,” J. Hepatology, 31., (Suppl. 1), pp. 17-24 (1999)]. Nearly four million individuals may be infected in the United States alone [M. J. Alter et al., “The Epidemiology of Viral Hepatitis in the United States, Gastroenterol. Clin. North Am., 23, pp. 437-455 (1994); M. J. Alter “Hepatitis C Virus Infection in the United States,” J. Hepatology, 31., (Suppl. 1), pp. 88-91 (1999)].
Upon first exposure to HCV only about 20% of infected individuals develop acute clinical hepatitis while others appear not to develop significant outward symptoms of infection. In almost 70% of instances, however, the virus establishes a chronic infection that persists for decades [S. Iwarson, “The Natural Course of Chronic Hepatitis,” FEMS Microbiology Reviews, 14, pp. 201-204 (1994); D. Lavanchy, “Global Surveillance and Control of Hepatitis C,” J. Viral Hepatitis, 6, pp. 35-47 (1999)]. This usually results in recurrent and progressively worsening liver inflammation, which often leads to more severe disease states such as cirrhosis and hepatocellular carcinoma [M. C. Kew, “Hepatitis C and Hepatocellular Carcinoma”, FEMS Microbiology Reviews, 14, pp. 211-220 (1994); I. Saito et. al., “Hepatitis C Virus Infection is Associated with the Development of Hepatocellular Carcinoma,” Proc. Natl. Acad. Sci. USA, 87, pp. 6547-6549 (1990)]. Unfortunately, there are no broadly effective treatments for the debilitating progression of chronic HCV.
The HCV genome encodes a polyprotein of 3010-3033 amino acids [Q. L. Choo, et. al., “Genetic Organization and Diversity of the Hepatitis C Virus.”Proc. Natl. Acad. Sci. USA, 88, pp. 2451-2455 (1991); N. Kato et al., “Molecular Cloning of the Human Hepatitis C Virus Genome From Japanese Patients with Non-A, Non-B Hepatitis,” Proc. Natl. Acad. Sci. USA, 87, pp. 9524-9528 (1990); A. Takamizawa et. al., “Structure and Organization of the Hepatitis C Virus Genome Isolated From Human Carriers,” J. Virol., 65, pp. 1105-1113 (1991)]. The HCV nonstructural (NS) proteins are presumed to provide the essential catalytic machinery for viral replication. The NS proteins are derived by proteolytic cleavage of the polyprotein [R. Bartenschlager et. al., “Nonstructural Protein 3 of the Hepatitis C Virus Encodes a Serine-Type Proteinase Required for Cleavage at the NS3/4 and NS4/5 Junctions,” J. Virol., 67, pp. 3835-3844 (1993); A. Grakoui et. al., “Characterization of the Hepatitis C Virus-Encoded Serine Proteinase: Determination of Proteinase-Dependent Polyprotein Cleavage Sites,” J. Virol., 67, pp. 2832-2843 (1993); A. Grakoui et. al., “Expression and Identification of Hepatitis C Virus Polyprotein Cleavage Products,” J. Virol., 67, pp. 1385-1395 (1993); L. Tomei et. al., “NS3 is a serine protease required for processing of hepatitis C virus polyprotein”, 3. Virol., 67, pp. 4017-4026 (1993)).
The HCV NS protein 3 (NS3) contains a serine protease activity that processes viral polyprotein to generate the majority of the viral enzymes, and is essential for viral replication and infectivity. The first 181 amino acids of NS3 (residues 1027-1207 of the viral polyprotein) have been shown to contain the serine protease domain of NS3 that processes all four downstream sites of the HCV polyprotein [C. Lin et al., “Hepatitis C Virus NS3 Serine Proteinase: Trans-Cleavage Requirements and Processing Kinetics”, J. Virol., 68, pp. 8147-8157 (1994)]. Substitutions of the catalytic triad of the HCV NS3 serine protease resulted in loss of viral replication and infectivity in chimpanzees [A. A. Kolykhalov et al., “Hepatitis C virus-encoded enzymatic activities and conserved RNA elements in the 3′ nontranslated region are essential for virus replication in vivo”, J. Virol., 74: 2046-2051]. It is known that mutations in the yellow fever virus NS3 protease decrease viral infectivity [Chambers, T. J. et. al., “Evidence that the N-terminal Domain of Nonstructural Protein NS3 From Yellow Fever Virus is a Serine Protease Responsible for Site-Specific Cleavages in the Viral Polyprotein”, Proc. Natl. Acad. Sci. USA, 87, pp. 8898-8902 (1990)].
The HCV NS3 serine protease and its associated cofactor, NS4A, processes the viral non-structural protein region into individual non-structural proteins, including all of the viral enzymes [C. Fulla, et al., “An amino-terminal domain of the hepatitis C virus NS3 protease is essential for interaction with NS4A”, J. Virol. 69, pp. 1769-1777; Y. Tanji et al., “Hepatitis C virus-encoded nonstructural protein NS4A has versatile functions in viral protein processing”, J. Virol. 69, pp. 1575-1581; C. Lin et al., “A central region in the hepatitis C virus NS4A protein allows formation of an active NS3-NS4A serine proteinase complex in vivo and in vitro”, J. Virol. 69, pp. 4373-4380], and is essential for viral replication. This processing appears to be analogous to that carried out by the human immunodeficiency virus aspartyl protease, which is also involved in processing of viral proteins. HIV protease inhibitors, which inhibit viral protein processing, are potent antiviral agents in man, indicating that interrupting this stage of the viral life cycle results in therapeutically active agents. Consequently it is an attractive target for drug discovery.
Several potential HCV protease inhibitors have been described in the prior art [PCT publication Nos. WO 02/18369, WO 02/08244, WO 00/09558, WO 00/09543, WO 99/64442, WO 99/07733, WO 99/07734, WO 99/50230, WO 98/46630, WO 98/17679 and WO 97/43310, U.S. Pat. No. 5,990,276, M. Llinas-Brunet et al., Bioorg. Med. Chem. Lett., 8, pp. 1713-18 (1998); W. Han et al., Bioorg. Med. Chem. Lett., 10, 711-13 (2000); R. Dunsdon et al., Bioorg. Med. Chem. Lett., 10, pp. 1571-79 (2000); M. Llinas-Brunet et al., Bioorg. Med. Chem. Lett., 10, pp. 2267-70 (2000); and S. LaPlante et al., Bioorg. Med. Chem. Lett., 10, pp. 2271-74 (2000)]. It is not known however whether these compounds would have the appropriate profiles to be acceptable drugs. Furthermore, it is possible that the HCV protease may become resistant to an otherwise acceptable drug.
Therefore, the current understanding of HCV has not led to any satisfactory anti-HCV agents or treatments. The only established therapy for HCV disease is interferon alpha-based treatment. However, interferons alpha have significant side effects [M. A. Walker et al., “Hepatitis C Virus: An Overview of Current Approaches and Progress,” DDT, 4, pp. 518-29 (1999); D. Moradpour et al., “Current and Evolving Therapies for Hepatitis C,” Eur. J. Gastroenterol. Hepatol., 11, pp. 1199-1202 (1999); H. L. A. Janssen et al. “Suicide Associated with Alfa-Interferon Therapy for Chronic Viral Hepatitis,” J. Hepatol., 21, pp. 241-243 (1994); P. F. Renault et al., “Side Effects of Alpha Interferon,” Seminars in Liver Disease, 9, pp. 273-277. (1989)] and induce long term remission in only a fraction (˜25%) of cases [O. Weiland, “Interferon Therapy in Chronic Hepatitis C Virus Infection”, FEMS Microbiol. Rev., 14, pp. 279-288 (1994)]. The current standard of care, pegylated interferon alpha in combination with ribavirin, has roughly 40-50% sustained viral response (SVR) for patients infected with genotype 1, which counts for 70% of chronic hepatitis C patients in developed countries, and 80% SVR in genotype 2 or 3 HCV-infected patients [J. G. McHutchison, et al., N. Engl. J. Med., 339: 1485-1492 (1998); G. L. Davis et al., N. Engl. J. Med., 339: 1493-1499 (1998)]. Moreover, the prospects for effective anti-HCV vaccines remain uncertain.
Thus, there is a need for more effective anti-HCV therapies, particularly compounds that inhibit HCV NS3 protease. Such compounds may be useful as antiviral agents, particularly as anti-HCV agents. An understanding of HCV resistance mutants would further progress towards effective HCV treatments.